The present invention relates to a rubber composition and a pneumatic tire using the same.
Recently, properties required for tires are diverse, including properties such as steering stability, abrasion resistance and ride quality in addition to low fuel costs, and in order to improve these performance, various devices have been made. Among these performances, in particular, both grip performance and rolling resistance property (low fuel cost performance) of a tire are properties relating to hysteresis loss of the rubber. In general, when the hysteresis loss is enlarged, grip force becomes high, and braking performance is improved, but rolling resistance is also enlarged and increase of the fuel cost is caused. Thus, since the grip performance is in antithetical relation with the rolling resistance property, various rubber compositions for a tire are proposed in order to simultaneously satisfy both properties.
For example, a method of compounding silica and a silane coupling agent has been known for the purpose of improving low exothermic property. The silane coupling agent prevents the coagulation among silica and improves processability by bonding with a silanol group on the surface of silica, and simultaneously, reduces the rolling resistance and improves abrasion resistance by chemically bonding silica and a polymer with the silane coupling agent. However, in order to attain these purposes, it is required that silica and a silane coupling agent are sufficiently reacted at a high temperature when they are kneaded, and a functional group reacting with a rubber in the silane coupling agent starts the reaction during processing such as kneading, which causes a problem that the phenomena of rubber scorch called gelation occurs. When kneading is carried out at a low temperature at which the rubber scorch does not occur, there is a problem that lowering of performance such as lowering of abrasion resistance occurs since the reaction of the silane coupling agent with silica is not adequate.
JP-A-2003-192842 discloses a rubber composition capable of improving wet grip performance without lowering the abrasion resistance and rolling resistance property by compounding a specified amount of specific anhydrous silica and hydrous silica and a pneumatic tire using the same, but it does not improve processability, and there is a room for improving rolling resistance property and wet grip performance.